1. Field of the Invention
This invention relates to an image signal processing apparatus. It has particular application to an image signal processing apparatus having an image pickup device and a color filter.
2. Description Related Art
In the prior art there is known an image pickup device which has a stripe color filter or a mosaic color filter and also there is known an image pickup device which has a "Bayer type" mosaic color filter as described in U.S. Pat. No. 3971,065.
In the Bayer type filter, the filter portions "Y" that pass luminance component of light are arranged offset in adjacent lines as shown in FIG. 2. Accordingly by adopting the Bayer type filter, the image pickup apparatus can achieve better resolution because it has a finer effective pitch for the Y filter portions. The finer effective pitch arises because the horizontal positions of the Y filter portions in one line are offset from the horizontal positions of the Y filter portions in the next line, and taking the two lines together a Y filter portion pitch can be achieved which is twice as fine as the pitch for one line alone.
However, in the above prior art Y filter portions have higher transparency than R or B filter portions, with the result that the image sensor tends to saturate more easily behind the Y filter portions than behind other filter portions. When the Y sensor portions saturate before other color sensor portions, false color signals tend to result, which is undesirable.
In order to solve this problem the color filter such as shown in FIG. 3 is known.
By adopting this kind of filter, color reproduction is improved, ut on the other hand spatial resolution tends to be reduced because the G signal replaces the Y signal in the output of the sensor. The Y signal can be obtained from the R, G and B signals, but the increase in effective Y resolution from the Bayer type filter is lost. This applies especially to an image having very little G signal, such as a predominantly red image.